Photoconductive layers have long been employed as a means for obtaining from a limited light exposure an image-wise pattern of conductivity which can be utilized in a number of electrolytic processes for generating visible, highcontrast, substantially permanent graphic images. Such photoconductive layers have thus been employed, for example, in imaging methods which entail electrolytically-induced polymerization, such as described in U.S. Pat. No. 3,436,215.
The present invention similarly involves electropolymerization of ethylenically unsaturated compounds, such as vinyl monomers, and in this respect is sufficiently closely related to the subject matter of the above-referenced patent that the disclosures and discussions there, particularly with respect to polymerizable monomers and photoconductive materials per se, will provide a significant and substantial description of the basis of the present invention.
The invention described in U.S. Pat. No. 3,436,215 is limited, for the most part, to a concomitant light exposure of a photoconductive cathode and applied DC voltage. In this regard, the prior procedure required a duration of light exposure determined by the polymerization rate of the particular composition employed. The present invention, on the other hand, is capable of generating polymeric images independently of the duration of light exposure, since, as will later be described, the procedure involves the use of a self-sustaining reaction of the generation of polymerization-inducing free-radical species, which reaction when once initiated by the electrolytic injection of metallic ions can proceed to completion without further photo-induced electrolysis.